Antitransmit-receive switch



31, 1954 w. c. CALDWELL ANTITRANSMIT-RECEIVE SWITCH Filed July 9, 1945 W n a :i 4: Lx q.

INVENTOR. WALLACE G. CALDWELL ATTORNEY Patentecl Aug. 31, 1954 ANTITRANSMIT-RECEIVE SWITCH Wallace 0. Caldwell, Boston, Mass, assignor, by mesne assignments, to the United States of America as represented by the Secretary of War Application July 9, 1945, Serial No. 604,016

1 Claim. 1

This invention relates to radio systems and more particularly to ultra high frequency systems involving wave guides.

In accordance with the present practice radar or radio locating equipment inoperation at the ultra high frequencies may use a common radiating and receiving antenna. In such instances the transmitted signal must use a channel which, in part, is common to a part of the received signal channel. To prevent damage to the receiver from the transmitted signals, transmit-receive or T-R devices are inserted in the receiver channel near the point of juncture of the two channels. To prevent loss of the received signal in the transmitter, antitransmit-receive or ATR devices are inserted in the transmitter channel near the point of juncture of the two channels. One type of T-R and ATR device which is used with Wave guides consists of a section of wave guide inserted in a series junction with the transmitter or receiver channel. As is well understood in the art, however, unless perfect contact is made between the T-R or ATR device and the wave guide, undesirable arcing will occur.

It has been found that if two ATR devices having the same resonant frequencies are used and placed approximately one-half wavelength apart a considerable increase in the band of frequencies over which the system will operate satisfactorily is achieved.

It is an object of the present invention, therefore, to provide an improved mount for a T-R or ATE tube in which arcing is minimized.

It is a further object of the present invention to provide an improved mount which permits two or more ATR tubes to be mounted within a minimum of space.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing in which:

Fig. l is a sectional view of the invention showing two ATR tubes mounted; and

Fig. 2 is a sectional view on line 2-2 of Fig. 1.

Referring now more particularly to Fig. 1, there is shown in cross-section a mount ll connected to a wave guide it and mounting ATR. tubes [3 and I l. The tubes l3 and M are essentially a section of wave guide I5 terminated at one end by a mounting flange H5 and at the other end by an iris 2|, the opening of which is sealed with a substance 22 such as glass. The tubes l3 and M are filled with an inert gas and sealed off by the plugs 23. The wave guide section I5 is effectively terminated by a plate 24 in which one or more openings such as opening 25 allow the gas to circulate freely. Screws 2% or other means are used to secure the tubes i3 and it to the mount II. The distance from the inside of the wave guide wall to the edge of the flange 56 is denoted by D.

In Fig. 2 there is shown a detailed view of one mount taken along the line 2-2 of Fig. 1. The section 3| is the narrow wall of the wave guide l2 and the section 32 is a portion of the mount H. A recess 33 cut in the wall 3| allows the tube l3 or it to be inserted to sufiicient depth in the mount it so that the iris 2i and seal 22 are flush with the broad wall of the wave guide iii. A recess 34 in the mount it prevents contact between the tube 53 or M and the mount H.

In the operation of this device including an ATR tube it is desired to have a minimum of reflection of energy back toward the source from the device during high level transmission and to have a maximum of reflection of energy back toward the source from the device during low level reception. The high level transmitted signal indicated by arrow 36 will cause the tubes it and M to are over across the opening of the iris 2!. The impedance of this are is very small, and since this are is effectively in series with the wave guide i2 the effect is as desired. In series with the are there exists an apparent open circuit between the walls of the mount II and tube 13 or M. If the distance D is made equal to an integral number of half wavelengths, the short circuit which exists between the wall of the mount H and the flange it will be transformed into a short circuit at the wall of the wave guide 12. It has been found that if D is equal to one-half wavelength, undesired characteristics are obtained as a function of frequency; however, these undesirable characteristics are not present if D is equal to one wavelength, and this length is, therefore, recommended. From the foregoing it is apparent that there has been obtained a minimum impedance in series with the wave guide, and the energy 36 will be transferred with a minimum of reflection. The action of the mount is the same for received signals, the only difference being that the tube does not arc over, and it, therefore, presents a high series impedance which causes a maximum of reflection. From Figs. 1 and 2 it will be seen that the ends of the tubes l3 and M are flush with the inner surface of the wave guide wall and therefore no physical discontinuities exist to cause undesirable reflections.

This mount may be used to cover another range of frequencies than that for which originally designed if the length D of the choke is altered. This may be achieved without altering the mount H by milling a recess in the flange of the tubes as indicated on tube It at 35 in Fig. 1. However, note that the two tubes are identical in any given instance and the milled recess is made in both or neither accordingly.

The terms transmit-receive switch and antitransmit receive switch, commonly referred to as TR and ATR switches, are used in the specification and claim with the following conventional means. A TR switch is an electronic switch which prevents the transmitted pulses from excessively overloading the radar receiver, but allows the received energy, which is much weaker, to reach the receiver without appreciable loss. It is placed in the Wave guide or transmission line adjacent the receiver and be tween the receiver and the antenna, which is used for both transmission and reception. The ATR switch is an electronic switch placed in the wave .guide or line adjacent the transmitter and between the transmitter and the antenna, and serves to effectively disconnect the transmitter 'from'the antenna during reception to prevent loss of the receivedsignal in the transmitter.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention.

What is claimed is:

In a radar system comprising a pulse transmitter and an antenna interconnected with a tubular wave guide having an opening in one wall thereof, an antitransmit-receive switch having a gas filled rectangular resonant cavity with an electrical gap included in said opening, a metallic rectangular enclosure consisting of side mounting flanges and an end plate, said switch being mounted inside said enclosure on said end plate and extending to the openin in said wall of the wave guide with the switch spaced from the wall of the wave guide and entirely external to the wave guide, said metallic enclosure and said resonant cavity being closely juxtaposed for a distance substantially equal to one wave length at the operating frequency of the wave guide so as to for-in a wave guide choke across the space between said switch-and the wall of the wave guide, said switch being positioned in the wall of said wave guide whereby high level transmission producesionization of the gas in said resonant cavity and. consequent closure of the gap which effectively closes said openin in the wall of the wave guide.

References Cited in the .file of this patent UNITED STATES PATENTS Number Name Date 2,190,668 Llewellyn Feb. 20, 1940 2,396,044 Fox Mar. 4, 1946 2,404,086 'O'kress July 16, 1946 2,408,055 Fiske Sept. 24, 1946 2,412,892 Ki'asil; Dec. 17, I946 2,415,962 Okress Feb. 18, 1947 2,442,118 Donal May 25, 1948 2,466,136 Tuller Apr. 5, 1949 

